Carrier system having variable power level for supervisory signaling



March 25, .1952 2,590,672

P. BAKKER CARRIER SYSTEM HAVING VARIABLE POWER LEVEL FOR SUPERVISORY SIGNALING Filed June 29, 1950 9 Sheets-Sheet l |se-l TRUNK CIRCUIT 20o 157N- WSNWA l AGK HGG I 172;: 413 a it) SUPY. 'MARG: I LINE BUSY E M65 l L152 U53 gar [ii I ns I |l79- JIM l; ,1 151/ Bi Rl60 I83 L175: v I I CORD CIRCUIT SLEEVE vlsz I lOl MANUAL EXCHANGE l0 Operator SW. Bd. I00

K I05 TALK KEY fi OPERATOR HAND SET A SUPY g lm r Lll2 INT. GEN. FlG.

INVENTOR. Pier Bakker BY v March 25, 1952 P. BAKKER 2, CARRIER SYSTEM HAVING VARIABLE POWER LEVPE FOR SUPERVISORY SIGNALING Filed June 29, 1950 9 Sheets-Sheet 2 TRUNK CIRCUIT 200 R 270 TALK I I l l l l l l l I I l a m/255 {0786 L E 0782 m 2. R250 227\ l zva/t ll- INVENTOR. Pler Bakker 9 Sheets-SAeet 3 INVENTOR;

Pier Bakker BY I M, oawwamz P. BAKKER CARRIER SYSTEM HAVING VARIABLE POWER LEVEL FOR SUPERVISORY SIGNALING Mairch 25, 1952 Filed June 29, 1950v m 4 w w A 3 m A. A Rr I l l\) w wd v w L. llfl'llll 5 2 v v 7 v 3 /l\ ..i|.... ll 0 R firm O N 3 3 0 I 3 CI H I r v s U 5 l 1 l l & v 4 31v 5 c 3 V K llllll II N U R l m m 3 b .m m K m .l 3 l I l l l l II M. a w c .7 2 3 a1 3 .v l H W 3 33 w h f 3 2 6 l 88 8 8 5 8 8 8 B C C C C c FIG. 3

P. BAKKER CARRIER SYSTEM HAVING VARIABLE POWER March 25, 1952 2,590,672

I I LEVEL FOR SUPERVISORY SIGNALING 9 Sheets-Sheet 4 Filed June 29, 1950 SWITCH F R 430 TALK cszm Attys 4 March 25, 1952 Filed June 29, 1950 P. lAKKER CARRIER SYSTEM AVING VARIABLE POWER LEVEL FOR SUPERVISORY SIGNALING 9 Sheets-Sheet 6 AUTOMATIC sw. APPARATUS 600 OUTGOING SELECTOR FINDER SELECTOR .o 602 60! e 605 i S6l6 ss|4 615 Q (1I LASS NE DISTRIBUTOR 3" m2 mcomme SELECTOR |-E 630 CF an CONNECTOE vso? 1:) AUTOMATlC EXCHANGE 2O INVENTVOR.

Pier 7 Bakker P. B AKKER CARRIER SYSTEM HAVING VARIABLE POWER March 25, 1952 LEVEL FOR SUPERVISOR! SIGNALING Filed June 29, 1950' 9 Sheets-Sheet 8 now mSOm 200mm www.57-

INVENTOR. Pier Bukker New 5:: 4 m2: 5 52. 55; m2: m: 8w wow 5:; 5:: 1023850 @0238: I 33 29km 83 562 208 9 I .5 wow 05 5985 m8 .5985 325850 I 555 @8338: I SE16 e 2w w r 5:; 5&8 1 a w 523823 WWW; m2 7 P P x 8mm wzazfi 5o .5? I zo m 3m v. 3 I Qmm. n Nm 42% 2 :3 i s n 9%; 2? Z8 3 IJI f 5:23 88 $8 83 $8 TRUNK CARRIER CIR. TERM.

March 25, 1952 I P. BAKKER 2,590,672

CARRIER SYSTEM HAVING VARIABLE POWER I LEVEL FOR SUPERVISORY SIGNALING 4 Filed June 29, 1950 9 Sheets-Sheet 9 OPER MANUAL EXC HANGE AUTOMATIC EXCHANGE SW 80. 2O

CARRIER TRUNK AUTO TERM. CIR. SW.

H.RF. H.PF.

VOICE FREQ. L.PF. L.P.E VO|CE FREQ.

EOUIF. L EQUIP FlG. IO

FIG. 9

Fig.| Fig.2 Fig.3 Fig-4 Fig-5 Fig.6

Fig. 7 Fig. 8

INVENTOR. Pier Bqkker Attys.

Patented Mar. "25, 1952 CARRIER SYSTEM HAVING VARIABLE POWER LEVEL FOR SUPERVISORY SIGNALING Pier Bakker, Chicago, 111., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application June 29, 1950, Serial No. 171,167

20 Claims. 1

The present invention relates to carrier current telephone systems, and more particularly to such a system involving a first exchange provided with an operator switchboard and a second exchange provided with automatic switching apparatus and subscriber substations.

It is a general object of the present invention to provide in a telephone system of the character noted, carrier current units in the respective exchanges that are selectively controlled for supervisory purposes primarily upon a marginal basis; i. e., upon the power level of the controlling carrier frequency signal in the associated carrier frequency signal circuit.

Another object of the invention is to provide in a telephone system of the character described, an improved arrangement for setting up connections in a simple and straightforward manner from the operator switchboard to any called one of the subscriber substations.

Another object of the invention is to provide in a telephone system of the character described, an improved arangement for setting up connections in a simple and straightforward manner from any calling one of the subscriber substations'to the operator switchboard.

A further object of the invention is to provide in a telephone system of the character described, an improved trunk circuit disposed between the operator switchboard and the associated carrier current terminal unit and an improved trunk circuit disposed between the automatic switching apparatus and the associated carrier current terminal unit.

I Further features of the invention pertain to the particular arrangement of the circuit elements of the telephone system, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which Figure is a diagrammatic illustration of a telephone system embodying the present invention and comprising a manual exchange lll and an automatic exchange 20; Figs. 1 to 8, inclusive, taken together, illustrate the details of the apparatus incorporated in the telephone system illustrated in Fig. 10 and embodying the features of the invention as briefly outlined above; and Fig. 9 illustrates the mode of combining Figs. 1 to 8, inclusive, to form a unified diagram.

More particularly, Fig. 1 illustrates the details of one of the cord circuits disposed at the operator switchboard in the manual exchange [0; Figs. 1 and 2, taken together, illustrate the details of a trunk circuit disposed in the manual exchange it Figs. 3 to 5, inclusive, taken together, illustrate the details of a trunk circuit disposed in the automatic exchange 26; Fig. 6 illustrates the general arrangement of the automatic switching apparatus disposed in the automatic exchange 20; and Figs. '7 and 8 respectively illustrate diagrammatically the carrier terminals respectively disposed in the manual exchange [0 and in the automatic exchange 28 and intercom nected by a line extending therebetween.

Referring now more particularly to Fig. 10, the telephone system there illustrated comprises a manual exchange lfl serving a group of subscriber substations, not shown, and an automatic exchange 20 serving a plurality of groups of subscriber substations, one of the groups including the subscriber substation T. The manual exchange it and the automatic exchange 20 are interconnected by a line lfil extending therebetween. The west end of the line it! terminates invoice frequency equipment 703 disposed in or beyond the manual exchange it; and the east end of the line Till terminates in voice frequency equipment 303 disposed in or beyond the automatic exchange 20. The manual exchange IB also comprises an operator switchboardlllfl; and the automatic exchange 20 comprises automatic switching apparatus 688.

The manual exchange H3 and the automatic exchange 29 are interconnected via the line 'Hll by a carrier current system. The carrier current system comprises an Adler type SD-l and includes carrier terminals Hi0 and 805) respectively disposed in the manual exchange In and in the automatic exchange 20. Also the manual exchange Ill comprises a trunk circuit 200 disposed between the operator switchboard i0 0 and the carrier terminal Hill; and the automatic exchange 29 comprising a trunk circuit 300 disposed between the automatic switching apparatus 600 and the carrier terminal 801]. More particularly the carrier terminal 100 disposed in the manualexchange it] comprises a high pass line filter W5 directly connected to the west portion of the line and a modulator filter m6 and a demodulator filter 1'01 connected in parallel to the high pass line filter 105. Also a low pass line filter N12 is connected between the west portion of the line l0! and the voice frequency equipment I03. Similarly the carrier and a modulator filter 806 and a demodulator filter 881 connected in parallel to the high pass line filter 805. Also a low pass line filter 802 is connected between the east portion of the line 10! and the voice frequency equipment 803.

Further the carrier terminal 100 comprises, as shown in Fig. '1, a modulator 108 connected to the modulator filter 106, and a carrier frequency generator 109 that is capable of generating both a normal frequency of 6800 cycles, and a dial frequency of 4845 cycles. Also the carrier frequency generator 109 is capable of generating the normal frequency of 6800 cycles both at a normal power and at a considerable increased or high power. The carrier frequency generator 109 is connected to the modulator 108, and the modulator is further connected to a hybrid coil 1I9, that is, in turn, connected to tip and ring conductors extending to the trunk circuit 200. Further, a balancing network 120 is connected to the hybrid coil 1 I 9. Also the carrier terminal 100 comprises a demodulator 1I0 connected to the demodulator filter 101, and a carrier frequency generator 1 that is capable of generating a frequency of 10,300 cycles. The carrier frequency generator 1 is connected to the demodulator H0, and the demodulator H is, in turn, normally connected via demodulator output filter 1I8 to the hybrid coil 'II9. Further the output circuit of the demodulator 1I0 is connected to the input circuit of an amplifier H2; and further the connection between the demodulator filter 101 and the demodulator 1I0 is directly connected to the input circuit of the amplifier H2; and the output circuit of the amplifier H2 is connected to the primary coil of a coupling transformer H3. The secondary coil of the coupling transformer H3 is connected commonly to two filters H4 and H5. The filter H4 is tuned to the carrier frequency of 10,300 cycles; and the filter H5 is tuned to the signal frequency of 1955 cycles. The filter H4 is further connected to the input circuit of an amplifier H6; and the filter H5 is further connected to the input circuit of an amplifier 1 I 1.

Further the carrier terminal 100 comprises a relay group, including a signal in relay R130, a supervisory relay R140, a talk relay R150, a signal out relay R160, and a supervisory relay R110. The output circuit of the amplifier H1 is connected to the winding of the signal in relay R130 and the output circuit of the amplifier H6 is connected to the winding of the supervisory relay R'I40. It is noted that the talk relay R150 is operative to interrupt the normal connection between the demodulator output filter H8 and the hybrid coil H9, and to complete an alternative balancing connection, including a resistor 155, to the hybrid coil H9. The signal out relay R160 is operative to detune the tank circuit of the carrier frequency generator 109 so as to alter the frequency thereof from the normal frequency of 6800 cycles to the dial frequency of 4845 cycles. As previously noted, the normal power of the carrier frequency generator 100 at the frequency of 6800 cycles may be substantially increased, and this is effected by operation of the supervisory relay R110. Finally, it is noted that the supervisory relay R140 is of the marginal type and is operative only in response to operation of the amplifier 1I6 to detect from the filter N4 the frequency of 10,300 cycles at the high power evel.

Further the carrier terminal 800 comprises, as shown in Fig. 8, a modulator 808 connected to the modulator filter 806, and a carrier frequency generator 809 that is capable of generatin both a normal frequency of 10,300 cycles, and a call frequency of 8345 cycles. Also the carrier frequency generator 809 is capable of generating the normal frequency of 10,300 cycles both at a normal power and at a considerably increased or high power. The carrier frequency generator 009 is connected to the modulator 808, and the modulator is further connected to a hybrid coil 8I9, that is, in turn, connected to tip and ring conductors extending to the trunk circuit 300. Further a balancing network 820 is connected to the hybrid coil 8I9. Also the carrier terminal 800 comprises a demodulator 8l0 connected to the demodulator filter 801, and a carrier frequency generator 8 that is capable of generating a frequency of 6800 cycles. The carrier frequency generator 8 is connected to the demodulator 8I0, and the demodulator 8I0 is, in turn, normally connected via a demodulator output filter 818 to the hybrid coil 8I9. Further the output circuit of the demodulator 8I0 is connected to the input circuit of an amplifier 8l2; and further the connection between the demodulator filter 801 and the demodulator 8l0 is directly connected to the input circuit of the amplifier BIZ; and the output circuit of the amplifier 8l2 is connected to the primary coil of a coupling transformer 8I3. The secondary coil of the coupling transformer 8I3 is connected commonly to two filters 8M and 8I5. The filter 8I4 is tuned to the carrier frequency of 6800 cycles, and the filter 8I5 is tuned to the signal frequency of 1955 cycles. The filter 8l4 is further connected to the input circuit of an amplifier BIG; and the filter M5 is further connected to the input circuit of an amplifier 8 I 1.

Further the carrier terminal 800 comprises a relay group, including a signal in relay R830, a supervisory relay R840, a talk relay R850, a signal out relay R860, and a supervisory relay R810. The output circuit of the amplifier 8I1 is connected to the winding of the signal in relay R830; and the output circuit of the amplifier 8; is connected to the winding of the supervisory relay R840. It is noted that the talk relay R850 is operative to interrupt the normal connection between the demodulator output filter 8I8 and the hybrid coil 8l9, and to complete an alternative balancing connection, including a resistor 855, to the hybrid coil 8I9. The signal out relay R860 is operative to detune the tank circuit of the carrier frequency generator 809 so as to alter the frequency thereof from the normal frequency of 10,300 to the call frequency of 8345 cycles. As previously noted, the normal power of the carrier frequency generator 809 at the frequency of 10,300 cycles may be substantially increased, and this is effected by operation of the supervisory relay R810. Finally it is noted that the supervisory relay R840 is of the marginal type and is operative only in response to operation of the amplifier 8I6 to detect from the filter 8I4 the frequency of 6800 cycles at the high power level.

In view of the foregoing, it will be understood that when the carrier terminal is the calling terminal, the signal out relay R is operated to detune the tank circuit of the carrier frequency generator 169 so that the dial frequency of 4845 cycles is generated and supplied to the modulator 108, whereby the lower side band of the dial frequency of 4845 cycles is supplied from the 5. modulator 108 via themodulator filter 106 and the high pass line filter 105 to the line 10I. At this time, the carrier terminal 800 is the called terminal, and the tank circuit of the carrier frequency generator 809 is tuned to produce the carrier frequency of 10,300 cycles and to supply this carrier frequency to the modulator 808, whereby the lower side band of the carrier frequency of 10,300 cycles is supplied from the modulator 808 via the modulator filter 808 and the high pass line filter 805 'to the line 18I. The supervisory relay R810 is selectively operative in order to cause the carrier frequency generator 808 to supply the carrier frequency of 10,300 cycles to the modulator 808 either at the normal power level or at the high power level, as previously noted. In the called carrier terminal 800, the carrier frequency of 4845 cycles supplied via the demodulator filter 801 to the demodulator 8|0 is beat therein with the carrier frequency of 6800 cycles supplied thereto from the carrier frequency generator 8H to produce the signal frequency of 1955 cycles, which signal frequency is ultimately detected and supplied to the winding of the signal in relay R830 for dial control purposes. the calling carrier terminal, the carrier frequency of 10,300 cycles supplied Via the demodulator filter 101 to the demodulator H is negated therein by the carrier frequency of 10,300 cycles supplied thereto from the carrier frequency generator 1| I. However, a small amount of this carrier frequency of 10,300 cycles is coupled directly from the connection between the demodulator filter 101 and the demodulator 'IIO to the amplifier H2 and ultimately detected and supplied to the winding of the supervisory relay R140. Since the supervisory relay R140 is of the marginal type, it is selectively operated only in response to the supply of the carrier frequency of 10,300 cycles into the amplifier H2 at the high power level, whereby the supervisory relay R140 is selectively controlled for supervisory purposes.

Also in view of the foregoing, it will be understood that when the carrier terminal 808 is the calling terminal, the signal out relay R880 is operated to detune the tank. circuit of the carrier frequency generator 808 so that the call frequency of 8345 cycles is generated and supplied to the modulator 808, whereby the lower side band of the call frequency of 8345 cycles is supplied from the modulator 808 via the modulator filter 808 and the high pass line filter 805 to the line At this time, the carrier terminal 100 is the called terminal, and the tank circuit of the carrier frequency generator 109 is tuned to produce the carrier frequency of 6800 cycles and to supply this carrier frequency to the modulator 108, whereby the lower side band of the carrier frequency of 6800 cycles is supplied from the modulator 108 via the modulator filter I06 and the high pass line filter 105 to the line 10I. The supervisory relay R810 is selectively operative in order to cause the carrier frequency generator 109 to supply the carrier frequency of 6800 cycles to the modulator 108 either at the normal power level or at the high power level, as previously noted. In the called carrier terminal 100, the call frequency of 8345 cycles supplied via the demodulator filter 101 to the demodulator H0 is beat therein with the carrier frequency of 10,300 supplied thereto from the carrier frequency generator 1| I to produce the signal frequency of 1955 cycles, which signal frequency is ultimately detected and supplied to the winding of the s snal in relay R130 for call control purposes. In the calling carrier terminal, the carrier frequency of 6800 cycles supplied via the demodulator filter 801 to the demodulator 8|0 is negated therein by the carrier frequency of 6800 cycles supplied thereto from the carrier frequency generator 8| I. However, a small amount of this carrier frequency of 6800 cycles is coupled directly from the connection between the demodulator filter 801 and the demodulator 810 to the amplifier 8 I2 and ultimately detected and supplied to the winding of the supervisory relay R840. Since" the supervisory relay R840 is of the marginal type, it is selectively operated only in response to the supply of the carrier frequency of 6800 cycles into the amplifier 8|2 at the high power level, whereby the supervisory relay R840 is selectively controlled for supervisory purposes.

As shown in Fig. l, the operator switchboard I00 is preferably of the multi-position type that includes the position illustrated, which comprises a number of cord circuits, including the cord circuit IOI, and standard common equipment, including a headset II3, a dial D|08 and an interrupter generator I01. Further the cord circuit |0| comprises two plugs PI 02 and PI 03, a dial key KI04 operative toconnect the dial D|08 thereto, a talk key KI05 operative to connect the headset I I3 thereto, and a ring key KI 06 operative to connect the interrupter generator I 01 thereto. Also, the cord circuit |0I comprises a supervisory lamp LI I I associated with the plug PI 02, a supervisory lamp LI I2 associated with the plug PI83, a supervisory relay RI30 associated with the supervisory lam LI.| I, a supervisory relay R|40 associated with the supervisory lamp LI I2, and a dial relay R|20 associated with the dial key K|04 and with the dial DI 08.

The trunk circuit 200, shown. in Figs. 1 and 2, is connected to the carrier terminal 100, as previously noted; and also the trunk circuit 200 terminates in a jack J I5I at the operator switchboard I00. The trunk circuit 200 comprises a line lamp LI52, a busy lamp LI 53, and a relay group, including a signal relay Rl55, ring-down relay RI80, a sleeve relay R|85, a supervisory relay RI10, a jack relay RI 15,. a control relay RI80, a signal in relay R2 I 0, a ring in relay R220, two supervisory relays R230 and R240, a hold relay R250, a busy relay R260, and a talk relay R210.

As, Shown in Fig. 6, the subscriber substation T has a subscriber line 8I0 extending thereto, with which a line circuit 6| I is individually associated. The automatic switching apparatus 600 comprises a plurality of groups of finder-selector links, each provided with an associated distributor, and corresponding to the groups of subscriber substations. One of the groups of finder-selector links includes the finder Bill and the selector 802, and is provided with the individually associated distributor 603; which group of finder-selector links is associated with the group of subscriber substations, including the subscriber substation T. Also the automatic switching apparatus 600 comprisesa plurality of groups of connectors respectively associated with the groups of subscriber substations. One of the groups of connectors includes the connector 801 and is associated with the group of subscriber substations, including the subscriber substation T. Also the automatic switching apparatus 600 comprises a group of outgoing selectors, including the outgoing selector 805, and an incoming selector 835. More particularly, the finder 68I of'the finder-selector link illustrated has access to the subscriber line 8|!) extending to the subscriber substation T, while the selector 602 of the finder-selector link illustrated has access to the connector 601 by way of the associated trunk 606, and has access to the outgoing selector 605, by way of the associated trunk 604. Also the outgoing selector 605 has access to the outgoing trunk 620 extending into the trunk circuit 300; while the incoming trunk 630 extending from the trunk circuit 300 is terminated in the incoming selector 635. Finally, the incoming selector 635 has access to the connector 601 by way of the associated trunk 606.

Preferably, the finders 60I, etc., the selectors 602, etc., the outgoing selectors 605, etc., the incoming selector 635, and the connectors 601, etc., are of the well-known Strowger type. Also the finder 60I comprises a plurality of sets of postnormal switch springs, one of which is indicated at $6. The sets of switch springs are actuated selectively in response to operation of the finder 60I different numbers of steps in the vertical direction in the selection of the corresponding ten line groups; and which sets of switch springs are connected to individually associated class tone conductors. Specifically, the set of switch springs S6I4 is actuated into closed circuit relation in order to connect the associated class tone conductor C6I3 to the associated condenser 6I5 when the finder GM is operated a predetermined number of steps in the vertical direction to select the ten line group of subscriber lines, including the subscriber line 6I0 extending to the subscriber substation T illustrated. Thus it will be understood that the subscriber substation T is in a given ten line group rendered a particular class of service, as indicated by the signal present on the class tone conductor G6 I 3.

Similarly, the selector 602 comprises a set of post-normal switch springs S6I6 which is actuated into closed circuit relation when the selector 602 is operated into a predetermined level to select the outgoing trunk 620, and indicative of a trunk call from the automatic exchange 20 to the manual exchange I0.

As shown in Figs. 3, 4 and 5, the trunk circuit 300 comprises a repeater 305 provided with coils 306 and 301 connected to the carrier terminal 800 and with coils 308 and 309 that are connected to an associated relay group. The relay group noted comprises a signal in relay R3 I 0, a talk relay R320, a supervisory relay R330, a signal out relay R340, a hold relay R350, a control relay R360, a supervisory relay R310, a ring out relay R380, a timer relay R4I0, a control relay R420, a switch relay R430, a seize relay R440, a ring out relay R450, a line relay R460, an answer relay R410, a supervisory relay R5|0, a tone relay R520, a timer relay R530, a hold relay R540, a busy relay R550, a control relay R560, and a reverse battery relay R510.

Again referring to- Fig. '1, the low pass line filter 102 is arranged to pass audio-frequency signals on the line I to the voice frequency equipment 103, and to block all of the high frequency carrier signals on the line 10I in order to prevent interference with the normal operation of the voice frequency equipment 103. The high pass line filter 105 is arranged to pass high frequency carrier signals in the overall range 4 kc. to 10.5 kc., and to block the passage of audiofrequency signals on the lin 10I in order to prevent interference with the carrier system. The modulator filter 106 is arranged to pass carrier frequency signals toward the lower end of the overall carrier frequency range and particularly the carrier frequencies between 4 kc. and 7 kc.,

8 and to block carrier frequency signals toward the upper end of the overall carrier frequency range and particularly the carrier frequencies between 7.5 kc. and 10.5 kc. On the other hand, th demodulator filter 101 is arranged to pass carrier frequency signals toward the upper end of the overall carrier frequency range and particularly the carrier frequencies between 7.5 kc. and 10.5 kc., and to block carrier frequency signals toward the lower end of the carrier frequency range and particularly the carrier frequencies between 4 kc. and 7 kc.-

Again referring to Fig. 8, the lower pass line filter 802 is arranged to pass audio-frequency signals on the line 10I to the voice frequency equipment 803 and to block all of the high frequency carrier signals on the line 10I in order to prevent interference with the normal operation of the voice frequency equipment 603. The high pass line filter 805 is arranged to pass high frequency carrier signals in the overall range 4 kc. to 10.5 kc., and to block the passage of audio-frequency signals on the line 10I in order to prevent interference with the carrier system. The modulator filter 806 is arranged to pass carrier frequency signals toward the high end of the overall carrier frequency range and particularly the carrier frequencies between 1.5 kc. and 10.5 kc., and to block carrier frequency signals toward the lower end of the overall carrier frequency range and particularly the carrier frequencies between 4 kc. and 7 kc. On the other hand, the demodulator filter 001 is arranged to pass carrier frequency signals toward the lower end of the overall carrier frequency range and particularly the carrier frequencies between 4 kc. and 7 kc., and to block carrier frequency signals toward the upper end of the carrier frequency range and particularly the carrier frequencies between '1.5 kc. and 10.5 kc.

A better understanding of the connection and arrangement of the apparatus incorporated in the telephone system illustrated in Fig. 10 and briefly described above will be facilitated from the following description of the extension of connections involving the manual exchange I0 and the automatic exchange 20.

Considering now the extension of a connection between the manual exchange I0 and the automatic exchange 20, assume that a call has been extended from a calling subscriber substation, not shown, in the manual exchange I0, to the operator switchboard I00 therein, and that the operator at the switchboard I00 has answered the call utilizing the cord circuit IOI. At this time, the plug PI03 of the cord circuit IOI has been inserted into the jack terminating the subscriber line extending to the calling subscriber substation and the talk key KI05 has been operated in order to connect the operator headset II3 to the cord circuit IOI. At this time, the operator at the switchboard I00 learns that the subscriber at the calling subscriber station in the manual exchange l0 desires to converse with a subscriber in the automatic exchange 20, such, for example, as the subscriber at the called subscriber substation T. The operator at the switchboard I00 observes the condition of the trunk circuit 200 as indicated by the corresponding busy lamp LI 53, and inserts the plug PI02 into the jack J I5I, assuming that the trunk circuit 200 is idle at this time, as indicated by the unlighted busy lamp LI 53.

When the plug PI02 is inserted into the jack JI5I, the contacts I5I thereof are operated, completing a circuit for operating the jack relay RI15 in the trunk circuit 200. Upon operating the jack relay RI15 completes, at the contacts 116. a circuit for illuminating the busy lamp LI53 in order to indicate the busy condition of the trunk circuit 200 at this time; also the jack relay RI15 completes, at the contacts I15, a series circuit for energizing the upper winding of the sleeve relay RI65 in the trunk circuit 200 and the winding of the supervisory relay RI30 in the cord circuit IOI, the circuit including the sleeve of the jack J II, the sleeve of the plug PI02, and the contacts l2I. When this series circuit is completed, the sleeve relay RI65 operates; however, the supervisory relay RI30 does not operate as it is of the marginal type. Upon operating, the sleeve relay RI65 completes, at the contacts I66 and I68, connections between the tip and ring conductors C185 and C184 and tip and ring of the jack I5I; and completes, at the contacts I65, a series circuit, including the contacts I18, 2, and 242, for energizing the winding of the supervisory relay RI and the upper and lower windings of the supervisory relay R230, this circuit also including the resistor 234. When this series circuit is completed, the supervisory relay R230 operates; however,

, the supervisory relay RI10 does not operate as it is of the marginal type. Upon operating, the supervisory relay R230 completes, at the contacts 233, a circuit for operating the hold relay R250. Upon operating, the hold relayR250 completes, at the contacts 25I, a circuit for energizing the winding of the talk relay R210 in order to cause the latter relay to operate shortly thereafter, it being of the slow-to-operate type. Also, upon operating, the hold relay R250 completes, at the contacts 255, a path, including the contacts MI and 226, for applying battery potential by way of the resistor 229 to the conductor C186 in order to effect energization of the winding of the signal out relay R160 in the carrier terminal 100 causing the latter relay to operate.

Upon operating, the signal out relay R1 60 completes, at the contacts 16I, the circuit for detuning the tank circuit of the carrier frequency generator 109 in order to cause the dial frequency 4845 cycles to be generated by the carrier frequency generator 109 and supplied to the modulater 108. The dial frequency 4845 cycles is impressed by the modulator 108 via the modulator filter 106 and the high pass line filter 105 upon the line 10I. The dial frequency 4845 cycles is impressed from the line 10I via the high pass line filter 805 and the demodulator filter 801 upon the demodulator 8I0 in the carrier terminal 800. In the demodulator 0I0, the dial frequency 4845 cycles is beat with the carrier frequency 6800 cycles produced by the carrier frequency generator BI I that is connected thereto in order to produce the signal frequency 1955 cycles. This signal frequency 1955 cycles is amplified by the lamplifier BIZ and impressed upon the primary coil of the coupling transformer 8I3, whereby the secondary coil of the coupling transformer 8I3 impresses this signal frequency 1955 cycles upon both of the filters 8I4 and 8I5. The filter 8I5 is tuned to the signal frequency 1955 cycles so that this signal frequency passes therethrough and is impressed upon the amplifier M1. The amplifier 8H detects the signal frequency 1955 cycles and effects energization of the winding of the signal in relay R330 causing the latter relay to operate.

Upon operating, the signal in relay R830 completes, at the contacts 83!, a path for grounding the conductor C33I in order to complete a circuit 'R3I0 in the trunk circuit 300 causing the latter relay to operate. Upon operating, the signal in relay R3l0 completes, at the contacts 3I4, a circuit for operating the hold relay R350. Upon operating, the hold relay R350 completes, at the contacts 35I and 353, a path, including the contacts 3I2, for applying ground potential by way of the upper winding of the supervisory relay R310 to the dial conductor C40I and battery potential is applied by way of the lower winding of the supervisory relay R5I0, the contacts 412 and 463 and the resistor 425 and the contacts I and 44! to the dial conductor C40I; whereby the upper winding of the supervisory relay R310 and the lower winding of the supervisory relay R5I0 are energized in series circuit relation, causing the relays noted to operate. In passing, it is pointed out that the upper winding of the supervisory relay R310 is normally bridged by the resistor 314 having a high value of resistance and rendering the supervisory relay R310 of the marginal type. However, the supervisory relay R310 is operated in the present instance by virtue of the circumstance that the upper winding thereof is energized directly in series with only the lower winding of the supervisory relay R5I0.

Upon operating, the supervisory relay R5I0 completes, at the contacts 5I4, a circuit for operating the busy relay R550. Upon operating, the busy relay R550 completes, at the contacts 553, a path, including the contacts 564, for applying ground potential to the control conductor C62I of the outgoing trunk 620 in order to mark the trunk 620 as busy to the outgoing selectors 605, etc., having access thereto. Also, upon operating, the busy relay R550 completes, at the contacts 555, a circuit, including the contacts 563, for operating the switch relay R430. Upon operating, the switch relay R430 completes, at the contacts 438, a circuit for energizing the upper winding of the answer relay R410 rendering the latter relay operative in response to the subsequent energization of the lower winding thereof in a predetermined direction, the answer relay R410 being of the polarized type. Also the switch relay R430 completes, at the contacts 438, a parallel path for applying ground potential to the control conductor C63I of the incoming trunk 630 extending to the incoming selector 635. Further, the switch relay R430 interrupts, at the contacts 432, the normal connection between the winding of the line relay R460 and the talk conductor C3I6; interrupts, at the contacts 434, the normal connection between the impedance element M6 and the talk conductor C3I1; and completes, at the contacts 43I, 433, 435 and 436, a path for bridging the lower winding of the answer relay R410 across the line conductors of the incoming trunk 630 extending to the incoming selector 635. Specifically the line conductor of the trunk 630 is connected via the contacts 43I the conductor C3I5, the coil 308, the talk conductor C3I6, the contacts 433, the resistors M1 and M8, the lower winding of the answer relay R410, the contacts 435, the talk conductor 03", the coil 309, the conductor C3I3, and the contacts 436 and 5I2 to the line conductor of the trunk 630. When the lower winding of the answer relay R410 is thus bridged across the line conductors of the trunk 630 and ground potential is applied to the control confor energizing the winding of the signal in relay 13 ductor C63I of the trunk 630, the incoming selector 635 is seized and rendered responsive to the subsequent transmission of a digit thereto.

Upon operating, the supervisory relay R310 completes, at the contacts 312, a circuit, including the contacts 35I, for operating the control relay R360. Upon operating, the control relay R360 completes, at the contacts 36I, a holding circuit, including the contacts 35I, for energizing the winding thereof. Also upon operating, the hold relay R350 completes, at the contacts 355, a path, including the contacts 342 and 322, for applying ground potential to the conductor C883 in order to complete a circuit .for energizing the winding of the talk relay R850 in the carrier terminal 800, causing the latter relay to operate. Upon operating, the talk relay R850 interrupts, at the contacts 85I and 853, the normal connections between the demodulator output filter 8I8 and the hybrid coil 8| and completes, at the contacts 852 and 854, an alternative balancing connection, including the resistor 855, to the hybrid coil 8I9. Further, upon operating, the hold relay R350 completes, at the contacts 354, a path, including the contacts 382, for applying battery potential via the resistor 381 to the conductor C881 in order to complete a circuit for energizing the winding of the supervisory relay R810 in the carrier terminal 800, causing the latter relay to operate.

Upon operating, the supervisory relay R810 completes, at the contacts 81!, the circuit for increasing the power of the carrier frequency generator 809 from the normal level to the high power level, whereby the carrier frequency 10,300 cycles at the high power level supplied by the carrier frequency generator 809 to the modulator 808 is impressed via the modulator filter 806 and the high pass line filter 805 upon the line I. The carrier frequency 10.300 cycles appearing upon the line ml is impressed via the hi h pass line filter 105 and the demodulator filter 101 upon the demodulator H0 in the carrier terminal 100. The carrier frequency 10,300 cycles impressed upon the demodulator H0 is negated by the carrier frequency 10,300 cycles connected to the demodulator H0 from the carrier frequency generator H I. However, a small portion of the carrier frequency 10.300 cycles is supplied directly from the connection between the demodulator filter 101 and the demodulator 1I0 to the amplifier 1I2and amplified and supplied to the primary coil of the coupling transformer H3. The carrier frequency 10.300 cycles appearing upon the secondary coil of the coupling transformer 1| 3 is supplied to the filters 1M and H5. The filter 1| 4 is tuned to the carrier frequency 10.300 cycles, whereby the carrier frequency 10.300 cycles is detected by the amplifier 1I6 completing a circuit for ener izing the winding of the supervisory relay R140. Since the carrier frequency 10,300 cycles is detected at the high power level by the amplifier 1I6, sufficient current is supplied to the winding of the supervisory relay R140 in order to cause the latter relay to o erate. Upon operating, the supervisory relay R140 completes, at the contacts "I, a path for applying ground potential to the conductor C182 in order to complete a circuit for operating the supervisory re-- lay R240 in the trunk circuit 200. Upon operating, the supervisory relay R240 completes, at the contacts 24I, an alternative circuit for energizing the upper winding of the supervisory relay R230 in series with the winding of the supervisory relay Rl10; and interrupts, at the contacts 242, the original circuit for energizing in series the upper and lower windings of the supervisory relay R230 and the winding of the supervisory relay Rl10. When the upper winding of the supervisory relay R230 is thus energized alone in series with the winding of the supervisory relay RI10, the supervisory relay R230 is retained in its operated position and the supervisory relay Rl10 is operated, the supervisory relay Rl10 being of the marginal type. Upon operating, the supervisory relay Rl10 completes, at the contacts I1 I a circuit for operating the control relay RI80. Upon operating, the control relay RI completes, at the contacts I8I, a termination circuit, including the resistor I12 and the condenser I13, across the tip and ring conductors C185 and C184. Also the control relay RI80 completes, at the contacts I82, a circuit for energizing the lower winding of the sleeve relay RI60 in multiple with the upper winding thereof and consequently in series with the winding of the supervisory relay RI30 in the cord circuit I M. When the upper and lower windings of the sleeve relay RI65 are thus energized in multiple and in series with the winding of the supervisory relay RI30, the sleeve relay RI65 is retained in its operated position and the supervisory relay RI30 is operated, the supervisory relay RI30 being of the marginal type. Upon operating, the supervisory relay RI 30 completes, at the contacts I3I, a circuit for illuminating the supervisory lamp LI II in the cord circuit IN and associated with the plug PI 02. The illumination of the supervisory lamp LI I I indicates to the operator at the switchboard IOI that the carrier equipment has operated between the trunk circuits 200 and 300 to seize the incoming selector 635 in the automatic exchange 20 and that the directory number of the called subscriber substation T may be dialed at this time.

The operator at the switchboard I00 operates the dial key KI04 and then proceeds to operate the dial DI08 in accordance with the first digit of the directory number of the called subscriber substation T in the automatic exchange 20. When the dial DI08 is thus operated, the off-normal springs I 09 thereof are first actuated into enga ement, thereby to complete a circuit, including the right-hand contacts of the dial key KI04, for operating the dial relay RI20 in the cord circuit IOI. Upon operating, the dial relay RI20 interrupts, at the contacts I2I, the previously traced I series circuit for energizing the winding of the supervisory relay RI30 in the cord circuit IOI and the upper and lower multiple connected windings of the sleeve relay RI 65 in the trunk circuit R200, whereby the relays mentioned restore. Upon restoring, the supervisory relay RI30 interrupts, at the contacts I 3|, the previously mentioned circuit for illuminating the supervisory lamp LI II in the cord circuit IOI; and upon restoring, the sleeve relay R completes, at the contacts I61 and I69 an alternative circuit, including the contacts I18, 2I I, and MI for energizing the upper winding of the supervisory relay R230. The lastmentioned circuit also includes the tip and ring of the jack JI5I, the tip and ring of the plug PI02, the left-hand contacts of the dial key KI04 and the impulsing contacts I I 0 of the dial DI08. Further, the sleeve relay RI65 interrupts, at the contacts I66 and I68, the previously mentioned connections between the tip and ring of the jack J I51 and line conductors C and C184, extending to the hybrid coil 1I9. Finally the sleeve relay RI65 interrupts, at the contacts I65, the circuit for retaining operated the supervisory relay RI10. Upon restoring, the supervisory relay Rl10 interrupts, at the contacts I1I, the circuit for retaining operated the control relay RI80.

Upon restoring, the control relay RI80 interrupts.

ating the control relay R420.

at the operator switchboard 100 in the manual exchange 10. Each time the signal in relay R830 restores and then reoperates, it interrupts and then recompletes, at the contacts 831, the path for applying ground potential to the conductor C881, whereby the signal in relay R310 in the trunk circuit 300 follows. Each time the signal in relay R310 restores and then reoperates, it completes and then interrupts, at the contacts 311, a circuit, including the contacts 351, 321 and 311, for energizing the lower winding of the supervisory relay R310; and each time the signal in relay R310 restores and then reoperates, it interrupts and then recompletes, at the contacts 312, the previously-traced circuit for energizing the upper winding of the supervisory relay R310 in series with the lower winding of the supervisory relay R510. Accordingly, the upper and lower windings of the supervisory relay R310 are alternatively energized in order to cause the latter relay to remain in its operated position; however, the lower winding of the supervisory relay R510 is deenergized in accordance with the impulses of each digit. Thus the supervisory relay R510 follows the signal in relay R310, the supervisory relay R510 restoring and reoperating in order to interrupt and then to. recomplete, at the contacts 512, the loop circuit extending between the lower winding of the answer relay R510 and the incoming selector 635 via the line conductors of the trunk 630. The first time the supervisory relay R510 restores, it completes, at the contacts 513, a circuit, including the contacts 552, for oper- Upon operating, the control relay R420 completes, at the contacts 422, a path for short-circuiting the resistor 418, the lower winding of the answer relay R410 and the repeater coil 309 in order to improve impulsing over the line conductors of the trunk 630 extending to the incoming selector 635. Each time the supervisory relay R510 operates and then restores, it interrupts and then recompletes, at the contacts 513, the circuit for energizing the winding of the control relay R420; however, the latter relay is retained in its operated position during impulsing as it is of the slow-to-release type. Further, each time supervisory relay R510 restores and then reoperates, it interrupts and then recompletes, at the contacts 514, the circuit for energizing the winding of the busy relay R550 however, the latter relay is retained in its operated position during impulsing as it is of the slow-to-release type.

At the conclusion of the first digit, the supervisory relay R130 in the cord circuit 101 is re-. operated, and the sleeve relay R165, the supervisory relay R110, and the control relay R180 in the trunk circuit 200 are reoperated. The supervisory relay R230 in the trunk circuit 200 is retained in its operated position in order to retain operated the signal out relay R160 in the carrier terminal 100 so that the signal in relay R830 in the carrier terminal 800 is retained in its operated position so as to retain operated the signal in relay R310 in the trunk circuit 300. The signal in relay R310 retains operated the superto theincomingselector 635.

In view of the foregoing, it will be understood that the incoming selector 635 receives the first digit and operates to select the group of connectors, including the connector 601. The incoming selector 635 then operates automatically to select an idle connector in the group noted. For example, the incoming selector 635 may operate to select the trunk 606 extending to the conhector 601, whereby the connector 601 is seized and conditioned to be responsive to the second and third digits transmitted over the line 101. The second and third digits transmitted over the line 101, in the manner explained above, are received by the connector 601, whereby the connector 601 operates to select the subscriber line 610 extending to the called subscriber substation T in the automatic exchange 20. The connector 601 then operates automatically to test the idle or busy condition of the called subscriber substation T.

First assuming that the called subscriber substation T is idle at this time, battery potential appears upon the control conductor of the subscriber line 610 causing the connector 601 to operate in order to seize the subscriber line 610, whereupon ground potential in the connector 601 is applied to the control conductor of the subscriber line 610 in order to mark in the line circuit 611 the subscriber line 610 as busy to the other connectors in the group having access theretc). Also the connector 801 operates to project ringing current over the line conductors of the subscriber line 010 so as to operate the ringer at the called subscriber substation T, and to return ring-back tone current over the line conductors of the trunk 606 and consequently over the incoming selector 635 and the line conductor of trunk 630. This ring-back tone current transverses the coils 308 and 309 of the repeater 305 inducing a corresponding ring-back tone current in the coils 300 and 301 of the repeater 305 that are coupled via the condensers 303 and 304 and the tip conductor C885 and the ring conductor C884 to the hybrid coil 819 in the carrier terminal 800. The ring-back tone current is passed from the hybrid coil 819 to the modulator 808, whereby the carrier frequency 10,300 cycles is modulated thereby and impressed via the modulator filter 806 and the high pass line filter 805 upon the line 110.

The carrier frequency 10,300 cycles modulated by the ring-back tone current that is impressed upon the line 101 passes through the high pass line filter 105 and the demodulator filter 101 and is impressed upon the demodulator in the carrier terminal 100. The demodulator 110 demodulates the carrier frequency 10,300 cycles modulated by the ring-back tone current and impresses the resulting ring-back tone signal via the demodulator output filter 118 and the contacts 151 and 153 upon the hybrid coil 119, whereby the ring-back tone current transverses the line conductors C184 and C185 to the ring and tip of the jack J 151 and ultimately via the cord circuit 100 to the operator headset 113. The ring-back tone current received in the operator headset 113 indicates to the operator at the switchboard 100 that the called subscriber substation T in the automatic exchange 20 is being rung by the connector in the automatic switching apparatus 600.

When the subscriber at the called subscriber substation T in the automatic exchange 20 answers the call, the connector 601 switches through -to interrupt the projection of ringing current 13 at the contacts I8 I, the termination circuit across the line conductors C185 and C184; and interrupts, at the contacts I82, a further point in the circuit for energizing the lower winding of the sleeve relay RI 65.

Accordingly at this time, the circuit for energizing the upper winding of the supervisory relay R230 in the trunk circuit 200 includes the impulsing contacts IIO of the dial DI08 in the cord circuit IOI. Thus when the dial DI08 is released and returned back to its normal position, the impulsing contacts IIO thereof are operated into disengagement one or more times corresponding to the number of impulses in the digit dialed, effecting corresponding interruptions and recompletions of the above traced circuit for energizing the upper winding of the supervisory relay R230, whereby the supervisory relay R230 follows the impulses of the first digit of the directory number of the called subscriber substation T dialed by the operator upon the dial DI08 at the switchboard I00. At the conclusion of the first digit, when the dial DI08 in the cord circuit IOI is returned to its normal position, the impulsing contacts IIO thereof are maintained in closed circuit position and the off-normal contacts I09 thereof are actuated into disengagement in order to interrupt the circuit for maintaining energized the winding of the dial relay RI20. Shortly thereafter, the dial relay RI 20 restores as it is of the slow-to-release type, re-

completing, at the contacts IZI, the previously traced circuit for energizing in series the winding of the supervisory relay RI30 and the upper winding of the sleeve relay RI65. The sleeve relay RI65 reoperates; however, the supervisory relay RI30 does not immediately operate as it is of the marginal type. Upon reoperating, the sleeve relay RI65 recompletes, at the contacts I65, the circuit for energizing the winding of the supervisory relay RI10 in series with the upper winding of the supervisory relay R230 in order to retain the supervisory relay R230 in its operated position and to effect reoperation of the supervisory relay RI10. Also the sleeve relay RI65 again interrupts, at the contacts I61 and I69, the previously traced alternative dialing circuit for energizing the upper winding of the supervisory relay R230; and recompletes, at the contact I66 and I68, the previously mentioned connections between the tip and ring of the jack J II and the line conductors C185 and C184. Upon reoperating, the supervisory relay RI recompletes, at the contacts I1I the circuit for operating the control relay RI 80. Upon reoperating, the control relay RI80 recompletes, at the contacts I8I, the termination circuit across the line conductors C185 and C184; and recompletes, at the contacts I82, the previously-mentioned circuit for energizing the lower winding of the sleeve relay RI 65 in multiple with the upper winding thereof so as to retain operated the sleeve relay RI65 and to effect reoperation of the supervisory relay RI30. Upon reoperating, the supervisory relay RI 30 recompletes, at the contacts I 3|, the circuit for illuminating the supervisory lamp LI I I in order again to indicate to the operator at the switchboard I00 that the call has not yet been answered at the called subscriber substation T in the automatic exchange 20. In a similar manner, the operator at the switchboard I 00 dials the second and third digits of the directory number of the called subscriber substation T in the automatic exchange and then at the conclusion of the dialing of the third digit mentioned, she

restores the dial key KIM to its normal position so as to interrupt the previously traced bridge, including the impulsing contacts IIO of the dial DI08, between the tip and ring of the plug PI02 of the cord circuit IOI. At this time, the tip and ring of the plug PI02 are operatively connected by way of the condensers I32 and I33 to the tip and ring of the plug P I 03 and consequent- 1y by way of the contacts of the talk key KI05 to the operator headset I I3.

In view of the foregoing, it will be understood that the supervisory relay R230 in the trunk circuit 200 follows the three series of impulses comprising the three digits of the directory number of the called subscriber substation T in the automatic exchange 20. In each series of impulses, each time the supervisory relay R230 restores and then reoperates, it completes and then interrupts, at the contacts 233, the circuit for energizing the winding of the hold relay R250, whereby the hold relay R250 is retained in its operated position during impulsing as it is of the slow-to-release type. Also each time the supervisory relay R230 restores and then reoperates, it interrupts and then recompletes, at the contacts 23I, the path for applying battery potential by way of the resistor 229 to the conductor C186 in order to cause the signal out relay R160 in the carrier terminal to follow. The first time the supervisory relay R230 restores, it also completes, at the contacts 232, a circuit, including the resistor 229 and the contacts 254 and 252, for energizing the lower winding of the busy relay R260 causing the latter relay to operate. Upon operating, the busy relay R260 completes, at the contacts 263, a holding circuit, including the contacts 212, for energizing the upper winding thereof; and completes, at the contacts 262, a multiple holding circuit, including the contacts 260, for energizing the upper winding thereof.

Thus the supervisory relay R230 in the trunk circuit 300 follows the series of impulses comprising each digit and repeats them at the contacts 23! to the signal out relay R160 in the carrier terminal 100. Each time the signal out relay R160 restores and then reoperates, it interrupts and then recompletes, at the contacts 16I, the detuning circuit extending to the tank circuit of the carrier frequency generator 109, whereby the carrier frequency generator generates alternatively the dial frequency 4845 cycles and the carrier frequency 6800 cycles. Specifically, the carrier frequency generator 109 generates the dial frequency 4845 cycles when the signal out relay R100 is operated; and the carrier frequency generator 109 generates the carrier frequency 6800 cycles when the signal out relay R160 is restored. The dial frequency 4845 cycles and the carrier frequency 6800 cycles are impressed alternatively by the modulator 108 Via the modulator filter 106 and the high pass line filter upon the line Fill in accordance with the impulses of each digit as the signal out relay R follows.

In the carrier terminal 800, when the dial frequency 4845 cycles is impressed upon the demodulator 6I0, the signal frequency 1955 cycles is produced, whereby the signal in relay R830 is operated, as previously explained. On the other hand, when the carrier frequency 6800 cycles is impressed upon the demodulator 810 there is no signal frequency supplied to the amplifier 8I2, whereby the signal in relay R330 restores. Accordingly the signal in relay R830 follows the series of impulses comprising each digit, dialed over the subscriber line 610 extending to the called subscriber substation T, and to interrupt the return of the ring-back tone current over the trunk E and the previously traced connection to the operator headset 1 $3 at the switchboard 100 in the manual exchange 10. Also the connector liii'i operates to bring about the reversal of polarity over the lineconductors of the trunk tilt and consequently over the loop circuit extending back to the answer relay R610 in the trunk circuit 3%, whereby the answer relay R410 is poled to operate. Upon operating, the answer relay am completes, at the contacts 4'11, an alternative path for applying battery potential by way of the upper and lower windings of the supervisory relay R510 to the dial conductor C iill, this path includin .the resistor 425 and the contacts 403, 51 and 441. Also the answer relay R4110 interrupts, at the contacts 412, the original path for applying ground potential directly via the lower winding of the supervisory relay RENE and the resistor 125 to the dialconductor C501. Accordingly, at this time, the upper and lower windings oithe supervisory relay R510 are energized in series via the dial conductor Still with the upper winding of the supervisory relay R32 0, whereby the supervisory relay R540 is retained in its operated position and the supervisory relay Rii'iii is restored, t e supervisory relay Rtlu being of the marginal type.

at the contacts 373, a connection, includingthe contacts between the grounded control conductor 002i oi the trunk E and the lower winding of the ring out relay R330, whereby the lower winding of the ring out relay R380 is energized causing the latter relay to operate. Upon operating, the ring out relay R380 completes, at the contacts 303, a circuit, including the contacts' 351, 352 and 313, for operating the talk relay R3223. Upon operating, the tall: relay R320 completes, at the contacts 02' a holding circuit, including the contacts 332 and 351, for energizing the winding thereof. Also upon operating, the ring out relay R300 interrupts, at the contacts 382, the path for applying battery potential via the resistor 33? to the conductor C88?! in order to effect the restoration of the supervisory relay R8'i0 in the carrier'terminal 800. Also upon operating, the talk relay R320 interrupts, at the contacts 023, the path for applying ground'potential to the conductor C883 in order to etject the restoration of the talk relay R350 in the carrier terminal see.

Upon restoring, the talk relay R850 interrupts, at the contacts 852 and 054, the balancing connection, including the resistor 855, to the hybrid coil 850; and recompletes, at the contacts 851 and 853, the normal connections between the demodulator output filter B1B and the hybrid coil 01.5. Also upon restoring, the supervisory relay R310 interrupts, at the contacts 8'11, the circuit for causing the carrier frequency generator 809 to generate'the carrier frequency 10,300 cycles at the high power level, whereby the carrier frequency generator 800 is now operated to generate the carrier frequency 10,300 cycles at the normal power level. When the carrier fre-' quency 10,300 cycles is impressed upon the line 10! at the normal power level, the output of the amplifier 112 in the carrier terminal l is reduced to a negligible value, whereby the output of the amplifier '110 is reduced to a small value so that the supervisory relay R1413 -restores, the supervisory relay Ri mbeing ofthe Upon restoring, tie supervisory relay R310 completes,

marginal type. Upon restoring, the supervisory relay R interrupts, at the contacts 141,, the path for applying ground potential to thegconductor C182 in order to cause the supervisoryre I lay R240 in the trunk circuit 200 torestore.

Upon restoring, the supervisory relay R 240 interrupts, at the contacts 241, the direct circuit for energizing the upper winding of the super visory relay R; and recompletes, at the'contacts 242; the circuit for energizing the upper and lower windings of the supervisory relay R230 in series with the winding of the supervisory-relay R110. Accordingly, the supervisory relay R230 is retained in its operated position, while the supervisory relay R110 restores, as it is of the marginal type. Upon restoring, the supervisory relay R170 interrupts, at the contacts 111, the circuit for retaining operated the con:- trol relay R180. Upon, restoring, the control relay R interrupt-s, at the contacts 181, the termination circuit across the line conductors CH0 and C180; and interrupts, at the contacts 132, the circuit for energizing the lower winding of the sleeve relay R165 in multiple with the upper winding thereof. Accordingly, at this time, only the upper winding of the sleeve relay R165 is energized in series, with the Winding of the supervisory relay R130, whereby the sleeve relay RIG5 in the trunk circuit 2001s retained in its cperatedposition and the supervisory relay R130 in the cordcircuit 101 restores, as itjisof the marginal type. Upon restoring the super.- visory relay R130. interrupts, atthe contacts 131,

the circuit for illuminating the supervisorylamp L111 associated with the plug P102 in order to render to the operator at the switchboard 1,00 answer-supervision. At this time th'enoperator at the switchboard 100 may converse with, the subscriber at the called subscriber substation T in. the automatic exchange 20 and. with the.

subscriber at the calling subscriber substation in the manual exchange l0, since a three-way communication connection has now been. established. Then theoperator may restore the talk key X10501" the cord circuit .101 disconnectingthe operator headset 113 from thecord circuit 101, whereby a private connection is then completed, between the calling. subscriber substation in the manual exchange 10 and the called subscriber substation T in the automatic.

exchange 20. At this time, transmitter battery is supplied via the windings of the supervisory relay R140, the back. contacts of the ring key K105. and the'tip and ring of the-plug-Plllii to the callingsubscriber substation, whereby the supervisory relay RMB occupies its operated position maintaining interrupted, at the contacts 141, a circuit for illuminating the supervisory lamp L112 in the cord circuit 101. According ly, the extinguished supervisory lamp L112 and the extinguished.supervisory lampL-1 11 respec-' tively indicate that/the calling, subscriber substation in the manual exchange, it and the called subscriber substation T in the automatic. exchange 20 are included in the established connection.

At this time, audio-frequency signals received from the calling subscriber substation in the manual exchange 11) pass through the cord circuit/E01 and thence over the tip and ring of the jack J 151 and the line conductors C185. and C784 to the hybrid coil '1 1 0 in the carrier-terminal 100. The audio-frequency signals then pass into the modulator 103' eiiecting-corresponding modulation of the-dial frequency 4845 cycles that is impressed at this time upon the line TM. The dial frequency 4845 cycles modulated by the audio-frequency then passes over the line ml and ultimately into the demodulator 8I0 in the carrier terminal 800, wherein the dial frequency noted is demodulated and the resulting audiofrequency signals are passed via the demodulator output filter 8I8 and the contacts 85I and 853 to the hybrid coil 8I0. The audio-frequency signals from the hybrid coil 8I9 then transverse the conductors C884 and C885, the condensers 303 and 304, and the coils 308 and 301 of the repeater 305 in the trunk circuit 300. Corresponding audio-frequency signals are generated in the coils 308 and 309 of the repeater 305 and are impressed upon the line conductors of the trunk 630, and thence pass over the incoming selector 635, the trunk 606, the connector 601 and the subscriber line 6I0 to the called subscriber sub-station T in the automatic exchange 20.

Also at this time, audio-frequency signals received from the called subscriber substation T in the automatic exchange 20 pass over the subscriber line 6I0, the connector 601, the trunk 606, the incoming selector 635 and the line conductors of the trunk 630 and the coils 308 and 309 of the repeater 305 in the trunk circuit 300. Corresponding audio-frequency signals are generated in the coils 306 and 301 of the repeater 305 and pass via the condensers 303 and 304 and the line conductors C885 and C884 to the hybrid coil 8I9 in the carrier terminal 800 and thence to the modulator 808. The carrier frequency 10,300 cycles is modulated by the audio-frequency signals and the resulting carrier frequency 10,300 cycles modulated by the audio-frequency signals is impressed upon the line 10I and ultimately passes to the demodulator H in the carrier terminal 100. The carrier signal noted is demodulated in the demodulator 1 I 0 and the resulting audio-frequency signals are passed via the demodulator output filter H8 and the contacts HI and 153 to the hybrid coil H9. The audio-frequency signals pass from the hybrid coil 1I9 via the line conductors C184 and C185 and the contacts I66 and I68 to the tip and ring of the jack J I 5| and thence via the cord circuit IOI to the calling subscriber substation in the manual exchange I8.

Now assuming that the called subscriber substation T in the automatic exchange 20 is busy when the connector 601 operates, in the manner previously explained, to select the subscriber line 8| 0 extending thereto, the connector 601 operates in order to cause busy-tone current to be returned over the previously-traced connection, including the trunk circuit 300 to the hybrid coil 8I9 in the carrier terminal 800 The carrier frequency 10,300 cycles is modulated in the modulator 808 by the busy-tone current, whereby the 6 resulting carrier signal is impressed upon the line 10I. The carrier frequency 10,300 cycles modulated by the busy-tone current is demodulated in the demodulator H0 in the carrier terminal 100 and the resulting busy-tone signal is returned overthe trunk circuit 200 and the cordcircuit IOI to the operator headset H3 at the switchboard I00, in the manner previously explained. At this time, the operator at the switchboard I00 advises the subscriber at the calling subscriber substation in the manual exchange I0 that the desired connection cannot be had immediately due to the busy condition of the called subscriber substation T in the automatic exchange 20, and

then proceeds to withdraw the plugs PI03 and 20 PI02 of the cord circuit IOI from the associated jacks. When the plug PI02 is withdrawn from the jack J I 5I, the apparatus involved in the connection extending toward the called subscriber substation T in the automatic exchange 20 is released in a manner more fully described hereinafter; and when the plug PI03 is withdrawn from the associated jack, the connection to the calling subscriber substation in the manual exchange I 0 is taken down.

At the conclusion of the connection, when the subscriber at the calling subscriber substation in the manual exchange I0 replaces the receiver of the telephone instrument thereat upon its associated switchhook, the previously-mentioned circuit for maintaining operated the supervisory relay RI40 in the cord circuit IOI, is interrupted. whereby the latter relay restores to complete, at the contacts I4I, the previously mentioned circuit for illuminating the supervisory lamp LI I2 in the cord circuit IOI. The illumination of the supervisory lamp LII2 renders to the operator switchboard I00 disconnect supervision, whereupon the operator at the switchboard I00 withdraws the plug PI03 of the cord circuit IOI from the associated jack taking down the connection to the calling subscriber substation in the manual exchange I0.

First assuming that the subscriber at the called subscriber substation T in the automatic exchange 20 replaces the receiver of the telephone instrument thereat upon its associated switchhock before the operator at the switchboard I00 withdraws the plug PI02 of the cord circuit IOI from the associated jack J I5I terminating the trunk circuit 200, the connector 601 operates to reverse the polarity over the trunk 606, the incoming selector 635 and the incoming trunk 630 to the lower winding of the answer relay R410 in the trunk circuit 300, causing the latter relay to restore as it is of the polarized type. Upon restoring, the answer relay R410 interrupts, at the contacts 41I, the path for applying battery potential via the upper and lower windings of the supervisory relay R5I0 upon the dial conductor C40I; and recompletes, at the contacts 412, the path for applying battery potential via the lower winding of the supervisory relay R5I0 to the dial conductor C40I. Accordingly, at this time, the lower winding of the supervisory relay R5I0 is energized in series with the upper winding 01' the supervisory relay R310 causing the latter relay to operate since it is of the marginal type. Upon operating, the supervisory relay R310 interrupts, at the contacts 313, the circuit for energizing the lower winding of the ring out relay R380 in order to cause the latter relay to restore. Upon restoring, the ring out relay R380 recompletes, at the contacts 382, the previously-traced path for applying battery potential to the conductor C881 in order to effect reoperation of the supervisory relay R810 in the carrier terminal 800.

Upon reoperating, the supervisory relay R810 in the carrier terminal 800 efiects the operation of the carrier frequency generator 800 to produce the carrier frequency 10,300 cycles at the high power level in order to effect reoperation of the supervisory relay R140 in the carrier terminal in the manner previously explained. Upon reoperating, the supervisory relay R recompletes, at the contacts 14I, the path for applying ground potential to the conductor C182 in order to effect reoperation of the supervisory relay R240 in the trunk circuit 200. Upon reoperating, the supervisory relay R240 recompletes, at the contacts 24!, the-gcircuitgforenergizing only the upperwinding of-the' supervisory relay R230 inseries with the winding of the supervisory relay Rl10;

and interrupts, at the contacts 242, the circuit for contacts I82, the circuit for energizing the lower winding of the sleeve relay R165 in multiple with the-upper winding thereof, whereby the sleeve relay RI65 is retained in its operated position and the supervisory relay Rl30 in the cord circuit I01 is'reoperated. Upon reoperating, the supervisoryrelay R130 again illuminates the super-- visory lamp Ll H in order to render to the operator at the switchboard I disconnect supervision.

Upon receiving disconnect supervision, the'operator at the switchboard 100 withdraws the plug- Pl02 of the cord circuit l0l from the associated jack J I51, thereby interrupting the series circuit for maintaining operated the sleeve relay R165 in the trunk circuit 200 and the supervisory re:- lay R130 in the cord circuit ml. The supervisory: relay R130 restores to interrupt, at the contacts I31, the circuit for illuminating the supervisory lamp Llll, whereby the cord circuit I01 isrestored to its normal idle condition. Also, when the plug PI02 is withdrawn from the jack J'l5l, the contacts l5l' thereof are operated into open circuitrelation interrupting the circuit for maintaining operated the jackrelay R115 in the trunk circuit 200. Upon restoring the jack relay R115 interrupts, at the contacts 110, the circuit for illuminating the busy lamp L153 inorder to indicate that the trunk circuit 200 has been restored to its normal idle condition. Upon restoring, the sleeve relay Rl05 interrupts, at the contacts 105, the series circuit for maintaining operated the'supervisory-relaysR110 and R230. Upon restoring, the supervisory relay M interrupts, at the contacts 11!, the circuit for retaining operated the control relay Rl80. Upon restoring, the control relay R180 interrupts, at the contacts I81, the termination circuit across the, line conductors C185 and C184. Upon restoring, the supervisory relay R230interrupts, at the, contacts 233, the circuit for energizing the winding of the hold relay R250 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Also upon restoring, the supervisory relay R230 interrupts, at the contacts 23l, the path for applying battery potential to the conductor C180 in order to efiect the restoration of the signal out relay R100 in thecarrier terminal 100. Upon restoring, the hold relay R250 interrupts, at the contacts 25l, the circuit for retaining operated the talk relay R210; and completes, at the contacts 253, a path, including the contacts 204 and 232, for applying battery potential by way of the resistor 229 to the conductor C181, in order to effect operation of the supervisor relay R110 in the carrierterminal 100.

Upon restoring, the signal out relay R100 interrupts, at the contacts 1Bl, the circuit fordetuning the tank circuit of thecarrier frequency generator 109, whereby the carrier frequencygene crater- 109 lthen operates :to: generatethe carrier frequency 6800 cycles atv the :normaltpowentleyel.

Upon operating, the supervisoryrelay R110f:come. pletes, at the contacts 11!, thecircuit for causing;

the carrier frequency generator to generate the carrier frequency 6300 cycles at the high. power level. When the dial frequency 4845 cycles: is removed from the line 101, the signal frequency.

of 1955 cycles is no longer produced by-the detial output of the carrier frequency 6800, cycles thatis applie'dto the coupling transformer 813 and thence to" the filters 8M and 0E5, whereby. the amplifier 810 produces a substantial. output efiecting operation of the supervisory relay-R840,

the latter relay being of the marginal type. 'Ihlld in the" carrier terminal 800, the signalin relay R830 restores removing ground potential. from' the conductor C88! in order toeffect restoration of the signal in relay R310 in thetrunk circuit 300; and the supervisory relay R840 is operated in order tocomplete, at thecontacts 8M, a-patli.

for applying ground potential to the conductor C802 so as to operate the supervisory relay. R330 in the trunk circuit 300.

Upon restoring, the signal in re1ay'R3l0 interrupts,'at the contacts 3I4, the initial circuit forenergizing the winding of the hold relay R350; and upon operating, the supervisory relay R330 interrupts, at the contacts 335, the hold circuit for energizing the winding of the hold relay R350. Accordingly, the hold relay R350 restores shortly thereafter, it being of the slow-to-release type. Also upon operating, the supervisory relay R330 interrupts, at the contacts 332, the holding cir-- cult for energizing the winding of the talk relay R320 in order to cause the latter relay to restore shortly thereafter, it-being of the slow-torelease type. Upon restoring, the hold relay R350 interrupts, at the contacts 353, the path for ap-- plying ground potential byway of the upperwinding of the supervisory relay R310 to the dial conductor C40l, in order to effect the restoration of the supervisory relay R310 and thesupervisory relay R5). Also the hold relay R350 interrupts, at the contacts 351, the holding-circuit for retaining operated, the control relay R360; and interrupts atithe contacts 354, the path forapplying battery potential to the conductor 0081 so as to effect restorationof the supervisory relay R810 inthe carrier terminal 800. Upon restoring, the supervisory relayR5l0 interruptaifit. the contacts 5, the circuit for energizing the winding of the busy relay R550 in order tocause the latter relay to restore shortly thereafter, it beingof the slow-to-release type. Upon restoring, the busy relay R550 interruptsat thecOntacts 555, the circuit for retaining operatedthe switch relay R430; and interrupts, at the, con,- tacts 553,,the path for, applying groundpotential to the control conductor C62l of the trunk 620. Uponrestoring, the switch relayR430 interrupts, at, the contacts 431, 433, 435 and, 430, the connections between the lower winding of the answer relay R410 and the line conductors .of the trunk 630, extending to-the incomingse1ector 035. Further, the switch relay R430 inter rupts, at thecontacts 438, the circuit for energizing the upperwinding ofthe answer relay R410 and the multiple path for applying ground potential to the-control conductor of the-.;.trunk 6.30.:.;.extendins;;to;the incoming seleetorfli5 

